1. Field of the Invention
This invention relates to phase shift key (PSK) receivers. More particularly, the present invention relates to PSK receivers capable of being easily changed or programmed to different data frequencies without redesign or basic hardware modifications. Further, the present invention achieves acquisition of the data stream faster than prior art systems.
2. Description of the Prior Art
Prior art data acquisition systems or receivers, employed phase lock loops to acquire and lock onto the data stream. The acquisition time of such systems is a mathematical function of doppler shift divided by data rate. The larger this ratio becomes the more difficult it is to lock on to the carrier signal.
Prior art data acquisition systems employed frequency multiplication in the recover loop as will be explained in detailed examples provided hereinafter. As a result of performing multiplication in the recovery loops, the doppler shift ratio is effectively increased. In the case of Binary Phase Shift Keying (BPSK) this ratio is doubled or increased by a factor of two. In the case of Quadrature Phase Shift Keying (QPSK) the ratio is increased by a factor of four, thus making it more difficult and more timely to achieve acquisition of the data stream. In the prior art data acquisition systems it was necessary to change the design of the acquisition loop to achieve a change in the data rate. It would be extremely desirable to provide a variable frequency data rate receiver. Further it would be extremely desirable to provide a data acquisition loop in the variable rate receiver which does not increase the acquisition time due to multiplication of the doppler shift.